View Full Version : HPT and MPI testing. Why?
shadowspirit
03-13-24, 04:00
Some ARs advertise the barrel is high pressure tested (HPT) and magnetic particle inspected (MPI). IIRC, some advertise those same tests for the bolt carrier group and the bolt within the group.
Do performing these test give any benefit? If these tests are performed, do they weed out anything that would have led to a much shorter service life or the risk of catastrophic failure somewhere along the line?
Some ARs advertise the barrel is high pressure tested (HPT) and magnetic particle inspected (MPI). IIRC, some advertise those same tests for the bolt carrier group and the bolt within the group.
Do performing these test give any benefit? If these tests are performed, do they weed out anything that would have led to a much shorter service life or the risk of catastrophic failure somewhere along the line?
They weed out any material defects. Like you say... a barrel could burst if a crack in the steel wasn't identified. Maybe lysander can shed more intimate light on the rejection rate and such.
It's part of mil spec to keep parts suppliers honest, not required by a good company who tightly controls their raw materials. Knights Armament does not do HPT and IIRC has stated it cuts bolt life in half, they also warrant their bolts for +20,000 rounds.
It's part of mil spec to keep parts suppliers honest, not required by a good company who tightly controls their raw materials.
American Mediocrity and Contracts awarded to minorities! I remember this crap in the 90s with Sanchez and Coopers mags. As I understand it they would give the magazine tooling to various brown people so they could make money screwing up the military's magazines. American stupidity at its finest.
bamashooter
03-13-24, 10:18
Some ARs advertise the barrel is high pressure tested (HPT) and magnetic particle inspected (MPI). IIRC, some advertise those same tests for the bolt carrier group and the bolt within the group.
Do performing these test give any benefit? If these tests are performed, do they weed out anything that would have led to a much shorter service life or the risk of catastrophic failure somewhere along the line?
Some (very few) do all components. Most batch test. Primary reason is for liability and it also serves as a good marketing tool.
First off - MPI without HPT is pretty pointless.
If a parts is stressed (HPT), the weak areas will open up and become visible to some form of penetrant inspection. If the parts is never stressed the weal areas will never become visible.
Second, the point stressing the parts is some stuff is just not visible from the outside, (see Figure 1).
And third, the idea that a single 120% stress test will some how hurt the part is laughable. That's not how that works. Steel has a fatigue limit, if the stresses are below this limit, it will not fail due to fatigue. Small arms barrels live in this range. M16/AR bolts are subject to low cycle fatigue. This means the stresses in the bolt under normal operation exceed the yield strength in some areas, and eventually cracks will develop. Measured life expectancy of bolts (military bolts) has shown the first crack can show up as early as 5,000 rounds, and some bolts will last over 20,000 rounds. That one loading that was 20% higher than the average is not going to shift that huge uncertainty zone enough to be noticeable.
(If you honesty believe that an HPT will shorten the life of the part, don't ever go to your doctor for a medical stress test.)
. . . they also warrant their bolts for +20,000 rounds . . .
Please, provide a link to this. I have heard this over and over but their website states something completely different.
https://i.imgur.com/OKDbHvO.png
Figure 1
It's part of mil spec to keep parts suppliers honest, not required by a good company who tightly controls their raw materials. Knights Armament does not do HPT and IIRC has stated it cuts bolt life in half, they also warrant their bolts for +20,000 rounds.
There is only one place in the world to get Carpenter 158 steel - Carpenter Technologies Inc. I do not know how much tighter you can get on your raw materials . . .
Yet, many good companied feel that there is value added to HPT/MPI their bolts, and still manage to price them competitively at $60 - $80, only $10 to $20 more than the non-HPT/MPI bolts.
". . . penny-wise, pound foolish . . ."
HPT absolutely shortens the life of the bolt, and this was explicitly covered in a NDIA briefing.
What it does get you is assurance it will work out of the box, at the cost longevity. Probably a good idea if you want to be able to spit out a TDP to any vendor and have confidence in a QA/QC process.
You will see bolts for GPF contracts maintain the legacy HP/MPI and some to other units not specify this.
HPT absolutely shortens the life of the bolt, and this was explicitly covered in a NDIA briefing.
What it does get you is assurance it will work out of the box, at the cost longevity. Probably a good idea if you want to be able to spit out a TDP to any vendor and have confidence in a QA/QC process.
You will see bolts for GPF contracts maintain the legacy HP/MPI and some to other units not specify this.
Which NDIA Brief?
Please link.
alvincullumyork
03-14-24, 13:46
It's part of mil spec to keep parts suppliers honest, not required by a good company who tightly controls their raw materials. Knights Armament does not do HPT and IIRC has stated it cuts bolt life in half, they also warrant their bolts for +20,000 rounds.
I thought knights batch HPT their barrels and bolts. They would take certain percentage of a lot and test those and then throw them away.
It's part of mil spec to keep parts suppliers honest, not required by a good company who tightly controls their raw materials. Knights Armament does not do HPT and IIRC has stated it cuts bolt life in half, they also warrant their bolts for +20,000 rounds.I think Snow Colt skips HPT, too, don’t they?
I wonder if car companies over heat the brakes on ever new car to make sure it can handle normal heat, or if aircraft companies subject the landing gear of every new airplane to an impact higher than it ever would in real life to make sure it can handle a hard landing?
I understand the wisdom, kind of. It just feels like there has to be a better way to it. Like just get material that’s really good and quality controlled? Don’t machine it too fast, ect.
Maybe make the cam pin hole smaller and round the locking lugs? I realize after I typed that, it’s done by a company already. Cross comparability is an issue. It’s too bad it wasn’t the original design.
I wonder if car companies over heat the brakes on ever new car to make sure it can handle normal heat, or if aircraft companies subject the landing gear of every new airplane to an impact higher than it ever would in real life to make sure it can handle a hard landing?
I understand the wisdom, kind of. It just feels like there has to be a better way to it. Like just get material that’s really good and quality controlled? Don’t machine it too fast, ect.
Maybe make the cam pin hole smaller and round the locking lugs? I realize after I typed that, it’s done by a company already. Cross comparability is an issue. It’s too bad it wasn’t the original design.
Yes, as a matter of fact, certain life-limited components are proof loaded and inspected to verify integrity.
Turbine blisks, one-piece compressor rotors, hydraulic cylinders, pressure vessels, landing gear struts
On the ground based side of things, cranes are proof loaded above the maximum certified weight on a regular basis.
If the service load was close to the maximum allowable load, you might have a point about the proof load being damaging. However, stuff like bolts have a substantial safety factor in the design, so the proof load keeps even the proof loading from being damaging.
EDIT:
Machining at the correct speed does not preclude internal material flaws.
And last: Making the cam pin hole smaller just moves the weak point from the bolt to the cam pin.
the AR-15 Junkie
03-17-24, 14:17
When I was working on Minuteman Missiles in the Air Force decades ago the hoists that we used to raise the Nukes off the missiles were marked, Proof Load Test at Twice the Rated Capacity. That entire quote was painted on the hoists.
I dont care who makes it, raw material flaws can and do happen, and process control is a numbers game to minimize chances while remaining profitable.
I am still waiting for the answers to these two questions:
1) It has been claimed multiple times that Knight's guarantees their bolts for 20,000 rounds, where does Knight's state this?
2) Can anyone link to a technical report that states that proof testing measurably reduces part life?
1) It has been claimed multiple times that Knight's guarantees their bolts for 20,000 rounds, where does Knight's state this?
On their website.
https://www.knightarmco.com/our-products
Under SR-16:
The heart of the product line is the E3 bolt, a proprietary design with a 20,000+ round lifespan.
On their website.
https://www.knightarmco.com/our-products
Under SR-16:
That is not a guarantee, that's advertising.
That is not a guarantee, that's advertising.
Neat.
This is what they actually state in regards to their products:
Knight’s Armament Company & KAC / KMC Limited Warranty:
Products and firearms are warranted to be free from defects in material and workmanship. This warranty shall apply to the original owner for a period of 1 year from date of purchase or delivery. Any such defects of which KAC / KMC receives written notice within 1 year from the date of purchase by the original owner, will be remedied by KAC / KMC without charge.
https://www.knightarmco.com/returns-repairs
Our 5.56 (E3) bolts are pretty different than anything else out there in the 5.56 world. Rounded lugs for reduced stress risers in the bolt, reduced cam pin hole for a stronger web, repositioned extractor pivot position for better mechanical advantage on the extractor, and more reinforcement on the lugs beside the extractor. 20k bolt life on short barrel suppressed guns (yeah, springs still need to be changed at their normal intervals).
The SR-25 and the MWS bolt carriers were very similar, but then both took diverging but similar paths. The lug dimensions are close enough to at least be nominally cross-compatible. LMT does good stuff, I hold Carl and his crew in high regard.
You have a representative of KAC publicly endorsing a 20k round life with the bolts. It's a lifecycle that the company advertises and employees are on record endorsing.
It's not in their blanket warranty policy, but it is aggressively marketed as a key feature and is recycled in the industry as fact with their products.
So you're correct with the published warranty, and users who repeat the official statements of KAC employees are correct in assuming said public statements are made with a significant data pool of end users to support it.
Well, a 2007 test showed a standard M4 bolt has over a 15,000 mean rounds to replacement, during the test twenty M4 fired 36,000 rounds each and consumed 46 bolts. All of them needed at least one bolt, but some did go over 20,000 rounds.
Sounds like a gov study.. mean #'s are so wide ranging as to be essentially useless.
The far left side of the bell curve, first failures, would be more useful for preemptive replacement on an in-service weapon if one intended to substantially derisk having an operational failure.
Perhaps left of the modal (vs mean) if one wanted to save money on a parts replacement matrix for a schoolhouse weapon.. if willing to accept the downtime.
In a schoolhouse using m4a1w/ greentip, no F/A & no suppressors, 1st visually perceptible cracks would appear ~ 7500rds
Likely the #'s have shifted left with m855a1 being introduced.
A systemic answer would be to have a bolt that outlast the barrel, and to rigorously enforce discarding the bolt with mated barrel (when shot out). This would prevent unknown life bolts being circulated through your n.
Sounds like a gov study.. mean #'s are so wide ranging as to be essentially useless.
The far left side of the bell curve, first failures, would be more useful for preemptive replacement on an in-service weapon if one intended to substantially derisk having an operational failure. [1]
Perhaps left of the modal (vs mean) if one wanted to save money on a parts replacement matrix for a schoolhouse weapon.. if willing to accept the downtime.
In a schoolhouse using m4a1w/ greentip, no F/A & no suppressors, 1st visually perceptible cracks would appear ~ 7500rds [2]
Likely the #'s have shifted left with m855a1 being introduced. [3]
A systemic answer would be to have a bolt that outlast the barrel, and to rigorously enforce discarding the bolt with mated barrel (when shot out). This would prevent unknown life bolts being circulated through your n.[4]
1) The first failure was about 10,500, the next 15,00 or so, the most were in the 17,500 to 20,500 range, a few further out.
2) Is that from some study, your experience, or someone else's experience? And, what time frame?
3) The test was repeated in 2015, just to see if M855A1 changed things. Answer not really, but that report does not have near the raw data of the earlier one, so you can't calculate other things, you might want to.
4) That is basically what they do with the M4s.
In any case, I fail to see any evidence of HPT harming the bolts to any extent.
1) The first failure was about 10,500, the next 15,00 or so, the most were in the 17,500 to 20,500 range, a few further out.
2) Is that from some study, your experience, or someone else's experience? And, what time frame?
3) The test was repeated in 2015, just to see if M855A1 changed things. Answer not really, but that report does not have near the raw data of the earlier one, so you can't calculate other things, you might want to.
4) That is basically what they do with the M4s.
In any case, I fail to see any evidence of HPT harming the bolts to any extent.
To the underlined, that makes sense. As you stated, if you dont exceed the yield point, the effects would not be measurable - within the effects of all the other variables.
Which brings up a point, people want to fine tune minutia within a system that incorporates multiple variables, its not realistic without a single, dedicated test system, or massive identical case subjects under controlled circumstances
To the underlined, that makes sense. As you stated, if you dont exceed the yield point, the effects would not be measurable - within the effects of all the other variables.
Which brings up a point, people want to fine tune minutia within a system that incorporates multiple variables, its not realistic without a single, dedicated test system, or massive identical case subjects under controlled circumstances
Or, have a reasonably good mathematical model of the system, which for the gas system isn't that hard to do, one is available.
J. H. Spurk, "The Gas Flow in Gas Operated Weapons," Ballistic Research Laboratories Report No. 1475, February 1970 (https://apps.dtic.mil/sti/pdfs/AD0704342.pdf)
Nathan Gerber, "Sensitivity Study of Rifle Gas Systems," Ballistic Research Laboratories Report No. 1524, January 1971 (https://apps.dtic.mil/sti/pdfs/AD0880431.pdf)
W. M. Werner, "Comparison of a Theoretical and Experimental Study of the Gas System in the M16A1 Rifle," Ballistic Research Laboratory Report No. 1548, August 1971 (https://apps.dtic.mil/sti/pdfs/AD0731218.pdf)
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The thing that amuses me to no end are the people that insist that you have to stick to the MIL-Spec on minutia like the cadmium plated detents for the takedown and pivot pins, and then go on about how great their chrome-silicon springs are . . .
the AR-15 Junkie
03-22-24, 17:51
That 3rd link is excellent, especially what it says on page 39.
frankmissing
03-23-24, 02:04
You have a representative of KAC publicly endorsing a 20k round life with the bolts. It's a lifecycle that the company advertises and employees are on record endorsing.
It's not in their blanket warranty policy, but it is aggressively marketed as a key feature and is recycled in the industry as fact with their products.
So you're correct with the published warranty, and users who repeat the official statements of KAC employees are correct in assuming said public statements are made with a significant data pool of end users to support it.
I usually trust recommendations, but what is written in the guarantee is not always a fact!!
That 3rd link is excellent, especially what it says on page 39.
Wonder what the conclusion would be of a similar test done today with the current M4?
The thing that amuses me to no end are the people that insist that you have to stick to the MIL-Spec on minutia like the cadmium plated detents for the takedown and pivot pins, and then go on about how great their chrome-silicon springs are . . .I’ve been shouting from the rooftops for years that “newfangled fancy aftermarket” CS springs bring rust to the equation while solving no real-world problems. They will, of course, last a long time in the right conditions.
LMT e-bolts seem to last an absurdly long time, even with thousands of dangerously overpressure loads involved. I think both of mine have outlived 2 barrels each. I’m sure Knights bolts are the same, or more likely, “better”.
We’ve seen from my “who breaks bolts anyway” thread that this is irrelevant for the majority of people that start with a quality rifle, and bolts cost less than the ammo required to break them, even if you add barrel cost to that. Of course, one breaking at the time of Murphy’s choosing would be lame, so it’s reasonable to buy quality and have a maintenance and inspection plan. Not worth agonizing about, though.
People don't understand CS spring are pointless in a firearm. CS springs are no better than music wire, unless the environment is above 350° F. They are great for valve springs in engines because the internal temperature can be that high and since they live in a oil bath corrosion is not an issue.
Music wire and CS are better than stainless steel for life, but the benefits of corrosion resistance far outweigh that.
People don't understand CS spring are pointless in a firearm. CS springs are no better than music wire, unless the environment is above 350° F. They are great for valve springs in engines because the internal temperature can be that high and since they live in a oil bath corrosion is not an issue.
Music wire and CS are better than stainless steel for life, but the benefits of corrosion resistance far outweigh that.
I think the main reason people like the Sprinco action springs is because they are customizable with all the different size gas ports that are out there in the commercial market.
Not sure why Sprinco chose CS over stainless steel unless it was just the long life benefits.
Not sure why Sprinco chose CS over stainless steel unless it was just the long life benefits. Marketing. Also, my understanding is that of the same wire diameter, length, coils, etc, it produces a ~10% stiffer spring. Which is also marketing-friendly. Aftermarket stiffer springs also can cause properly designed rifles to have stoppages.
the AR-15 Junkie
03-23-24, 10:13
People don't understand CS spring are pointless in a firearm. CS springs are no better than music wire, unless the environment is above 350° F. They are great for valve springs in engines because the internal temperature can be that high and since they live in a oil bath corrosion is not an issue.
Music wire and CS are better than stainless steel for life, but the benefits of corrosion resistance far outweigh that
Like this?
https://i.imgur.com/zWRVOuC.jpeg
Marketing. Also, my understanding is that of the same wire diameter, length, coils, etc, it produces a ~10% stiffer spring. Which is also marketing-friendly. Aftermarket stiffer springs also can cause properly designed rifles to have stoppages.
The other place than CS is better than if the wire diameter is over 0.080", interestingly, the diameter of the action spring is 0.072", right at the crossover point.
https://cdn-0.mentoredengineer.com/wp-content/uploads/2019/11/strengthvsdia.png
If you make three action springs, one from 17-7 stainless, one from music wire, and one from chrome-silicon, here is what you get: (note, my spring calculator won't even bother to design a CS spring smaller than 0.080", so all have a wire diameter of 0.080")
OD: 0.995"
Wire Dia - .080"
Free length - 10.70"
Total coils - 38
Active coils - 36
Ends - closed
Material . . . . . . . . . . . . . . . . . . Music Wire . . . . . . . . . . . . Chrome-Silicon . . . . . . . . . . . 17-7 Stainless
Rate . . . . . . . . . . . . . . . . . . . . . 2.134 lb/in . . . . . . . . . . . . . . 2.134 lb/in . . . . . . . . . . . . . . . 2.038lb/in
Maximum Load . . . . . . . . . . . . 16.174 lb(f) . . . . . . . . . . . . . .16.174 lb(f) . . . . . . . . . . . . . . 15.447 lb(f)
Max Shear Stress . . . . . . . . . 133,480 psi . . . . . . . . . . . . . 133,950 psi . . . . . . . . . . . . . . 120,790 psi
If all we were worried about were the "springy qualities" of these, there is no clear winner, none of these are appreciably "better" than the others. However, if you throw in corrosion resistance, they rank (1) Stainless, (2) Music Wire, and a distance third (3) Chrome-Silicon. Yes, the stainless has a lower maximum shear allowable, but as soon as you get a corrosion pit in the others, that number will drop like a rock.
Is there was a milspec stainless steel variety of reduced power and extra power springs available like Sprinco has folks would probably drop CS like a rock.
The main attraction isn’t CS. It’s having the reduced & extra power options because of all the variation in commercial gas ports and because people just like to tweak things.
It is not mystical material properties that allows you to vary the spring properties. All you have to do is change the wire diameter, the number of coils, and/or the total length. You could also change the OD, but then you start having to major changes to the design.
It is not mystical material properties that allows you to vary the spring properties. All you have to do is change the wire diameter, the number of coils, and/or the total length. You could also change the OD, but then you start having to major changes to the design.
Thats my point. If you used the same Stainless steel material as a mil spec action spring but offered reduced and extra power versions to deal with the major changes in commercial gas ports folks would drop cs like a rock.
There's not much point in tweaking a Colt 6920. But many of the other commercial brands gas ports are all over the place. A $20 spring is more palatable than a new rifle or barrel.
the AR-15 Junkie
03-23-24, 12:32
My guess is most (not all) but most people running the Sprinco stuff are doing so because SOTAR pushes it and they don't know any better.
But, then you can pull the wool over people's eyes with statements like:
". . . . very high stress applications such as, NASCAR, Formula One, Moto GP & Pro Stock racing motor valve springs. It is not uncommon in some of these applications for valve springs to see 15,000,000 compression cycles in one race. It is this extraordinary capability that makes Chrome Silicon wire the obvious choice in our spring production vs. music wire or 17-7 PH used in OEM springs and by most aftermarket competitors. "
Never mind the fact that those springs are in a 350° F environment, constantly bathed in oil, are kept in well away from solid height*, and have wire diameters much larger than 0.08".
Face it, the average gun owner does not know enough about engineering to make logical engineering choices. A well written techno-babble laced advertisement, delivered by an ex-special forces "Operator", will win cash prizes every time.
https://www.youtube.com/watch?v=MXW0bx_Ooq4&t=44s
EDIT:
* Operation inside 130% of solid length is the major factor in the short life of recoil and magazine springs.
* Operation inside 130% of solid length is the major factor in the short life of recoil and magazine springs.
Does that argue for use of a flatwire spring with a shorter solid length, or do other stresses inherent in that design counteract the benefit?
Does that argue for use of a flatwire spring with a shorter solid length, or do other stresses inherent in that design counteract the benefit?
Why forcing a spring to go solid is bad:
The first reason is impact. In cyclic compression, the coils gain speed in the direction of compression, even if the force compressing the spring stops short of the solid length, the momentum of the coils can carry them further back until they bottom out. This can physically distort the coils depending on the speed. The other reason is the maximum twisting stress allowable. When a spring goes solid, its stress has usually gone past the fatigue limit*; depending on the spring design this can happen well above solid. If the stress exceeds the yield limit, the spring will take a permanent set.
If space is limited, flat wire springs work extremely well, however, you can still exceed maximum stress levels if you aren't careful. The only major problem with flat wire springs, aside from their expense, is you cannot get really stiff springs without high OD/ID ratios, or very thick sections (square profiles). Flat wire spring are generally less stressed. So, to the question I would say that flat wire springs offer many benefits at the sole disadvantage of cost.
_________________________
* Steels have a fatigue limit, if the stress can be held below this value, the item can endure an infinite number of loading cycles. If the stress is above the fatigue limit, but still below the yield strength, cyclic loading will be high-cycle fatigue, with the number of cycles in the 10^6 range. If the stress is above the yield, but still below the ultimate limit, it will be subject to low-cycle fatigue with the number of cycle in the 10 to 10^3 range.
jackblack73
03-24-24, 09:18
My guess is most (not all) but most people running the Sprinco stuff are doing so because SOTAR pushes it and they don't know any better.
Sprinco had been around for many years before SOTAR ever emerged on YouTube. I can remember reading about the recommended blue Sprinco spring and H2 buffer on this board well before the first SOTAR video. I live in a desert, BTW, so they work great for me.
Here's a pretty comparison and analysis of different action springs.
https://youtu.be/8fMVZbrnvu8?si=-I-6Dlqo3EaoniJ3
CrowCommand
03-24-24, 16:48
But, then you can pull the wool over people's eyes with statements like:
". . . . very high stress applications such as, NASCAR, Formula One, Moto GP & Pro Stock racing motor valve springs. It is not uncommon in some of these applications for valve springs to see 15,000,000 compression cycles in one race. It is this extraordinary capability that makes Chrome Silicon wire the obvious choice in our spring production vs. music wire or 17-7 PH used in OEM springs and by most aftermarket competitors. "
Never mind the fact that those springs are in a 350° F environment, constantly bathed in oil, are kept in well away from solid height*, and have wire diameters much larger than 0.08".
Face it, the average gun owner does not know enough about engineering to make logical engineering choices. A well written techno-babble laced advertisement, delivered by an ex-special forces "Operator", will win cash prizes every time.
https://www.youtube.com/watch?v=MXW0bx_Ooq4&t=44s
EDIT:
* Operation inside 130% of solid length is the major factor in the short life of recoil and magazine springs.
Wow am I that dumb, or Is that video a joke?
titsonritz
03-24-24, 17:06
My guess is most (not all) but most people running the Sprinco stuff are doing so because SOTAR pushes it and they don't know any better.
Iraqgunz was using and recommending them long before SOTAR, I’m pretty sure he knew better.
titsonritz
03-24-24, 17:13
Sprinco had been around for many years before SOTAR ever emerged on YouTube. I can remember reading about the recommended blue Sprinco spring and H2 buffer on this board well before the first SOTAR video. I live in a desert, BTW, so they work great for me.
My point.
Probably IG
Wow am I that dumb, or Is that video a joke?
Its a joke.
I have a sprinco spring in one rifle i installed before I found out about the EZTUNE tubes. I keep it oiled and it works fine
It's all about making sure everything's in top shape and reducing the chances of any nasty surprises popping up later on. Trust me, it's worth it for the extra peace of mind knowing your gear's solid.
shadowspirit
03-26-24, 05:29
People don't understand CS spring are pointless in a firearm. CS springs are no better than music wire, unless the environment is above 350° F. They are great for valve springs in engines because the internal temperature can be that high and since they live in a oil bath corrosion is not an issue.
Music wire and CS are better than stainless steel for life, but the benefits of corrosion resistance far outweigh that.
Aren't CS springs much better for life(number of compression/decompression cycles) than stainless and music wire? As for corrosion resistance, just spray/wipe some oil or other lube/protectant on it once in a while.
shadowspirit
03-26-24, 05:34
Why forcing a spring to go solid is bad:
The first reason is impact. In cyclic compression, the coils gain speed in the direction of compression, even if the force compressing the spring stops short of the solid length, the momentum of the coils can carry them further back until they bottom out. This can physically distort the coils depending on the speed. The other reason is the maximum twisting stress allowable. When a spring goes solid, its stress has usually gone past the fatigue limit*; depending on the spring design this can happen well above solid. If the stress exceeds the yield limit, the spring will take a permanent set.
If space is limited, flat wire springs work extremely well, however, you can still exceed maximum stress levels if you aren't careful. The only major problem with flat wire springs, aside from their expense, is you cannot get really stiff springs without high OD/ID ratios, or very thick sections (square profiles). Flat wire spring are generally less stressed. So, to the question I would say that flat wire springs offer many benefits at the sole disadvantage of cost.
_________________________
* Steels have a fatigue limit, if the stress can be held below this value, the item can endure an infinite number of loading cycles. If the stress is above the fatigue limit, but still below the yield strength, cyclic loading will be high-cycle fatigue, with the number of cycles in the 10^6 range. If the stress is above the yield, but still below the ultimate limit, it will be subject to low-cycle fatigue with the number of cycle in the 10 to 10^3 range.
Is loading a 30 round AR mag to 28 rounds instead of 30 and example of the above explanation? Will loading 28 rounds give the spring substantially longer life?
shadowspirit
03-26-24, 05:39
The other place than CS is better than if the wire diameter is over 0.080", interestingly, the diameter of the action spring is 0.072", right at the crossover point.
If you make three action springs, one from 17-7 stainless, one from music wire, and one from chrome-silicon, here is what you get: (note, my spring calculator won't even bother to design a CS spring smaller than 0.080", so all have a wire diameter of 0.080")
OD: 0.995"
Wire Dia - .080"
Free length - 10.70"
Total coils - 38
Active coils - 36
Ends - closed
Material . . . . . . . . . . . . . . . . . . Music Wire . . . . . . . . . . . . Chrome-Silicon . . . . . . . . . . . 17-7 Stainless
Rate . . . . . . . . . . . . . . . . . . . . . 2.134 lb/in . . . . . . . . . . . . . . 2.134 lb/in . . . . . . . . . . . . . . . 2.038lb/in
Maximum Load . . . . . . . . . . . . 16.174 lb(f) . . . . . . . . . . . . . .16.174 lb(f) . . . . . . . . . . . . . . 15.447 lb(f)
Max Shear Stress . . . . . . . . . 133,480 psi . . . . . . . . . . . . . 133,950 psi . . . . . . . . . . . . . . 120,790 psi
If all we were worried about were the "springy qualities" of these, there is no clear winner, none of these are appreciably "better" than the others. However, if you throw in corrosion resistance, they rank (1) Stainless, (2) Music Wire, and a distance third (3) Chrome-Silicon. Yes, the stainless has a lower maximum shear allowable, but as soon as you get a corrosion pit in the others, that number will drop like a rock.
How much more compression cycles can the CS springs last if corrosion is kept at bay? 2X? 3X? 4X?
How much more compression cycles can the CS springs last if corrosion is kept at bay? 2X? 3X? 4X?
How often do you wear out a stainless or music wire spring? I actually wear these out more than most, but not particularly often.
“Just put oil on it” is silly, because the action spring is not a place where lubrication would be required if we could just stop tinkering. Saying that it’s the solution, is admission that there’s a problem, and I’m saying that problem doesn’t need to exist, because CS springs don’t solve any problem.
BTW, I used a CS spring yesterday in a T&E gun. The reward was failures to lock back with a Velos.
Is loading a 30 round AR mag to 28 rounds instead of 30 and example of the above explanation? Will loading 28 rounds give the spring substantially longer life?
It loads easier on a closed bolt. As far as lifespan, magazine springs are easily replaced along with any other spring in the gun.
Aren't CS springs much better for life(number of compression/decompression cycles) than stainless and music wire? [1] As for corrosion resistance, just spray/wipe some oil or other lube/protectant on it once in a while.[2]
1) No, they are not. Unless you are comparing them in a high temperature environment, chrome-silicon spring are no different than music wire, and only marginally better than 17-7 stainless*.
2) The driver here seems that everybody wants to to have the longest lasting spring. The stress on a spring is highest on the surface of the spring wire. So, any cracks, flaws or other damage to the surface of the wire will be the initiation point for fatigue cracking. Chrome-silicon spring are not very corrosion resistant, so any small corrosion spot will start a fatigue crack.
The longest lasting spring would be a stainless steel spring. In a test of 20 Carbines and 3/4 of a million rounds, not one action spring failed.
Now, if you want to play with spring rates, and pre-loads, and C-S is the only offering available, that's fine, they will work just as well as anything else and last a long time if you take care of them. They might even be better because you can get the spring rate you want, but don't try and convince everyone they are better springs because they are C-S. They aren't.
_________________________
* Careful, there are two popular types of stainless steel for springs, 17-7 and 302/304. The 300 series stainless steels work harden only and not nearly as good as 17-7 stainless.
How much more compression cycles can the CS springs last if corrosion is kept at bay? 2X? 3X? 4X?
ZERO.
In a room temperature environment (0° to 200° F), and spring wire diameter less than 0.080", there is no difference between chrome-silicon and music wire. 17-7 stainless does not have quite as high a yield strength as music wire, it is strong enough, and even gets you a little of that high temperature operational envelope back.
* Careful, there are two popular types of stainless steel for springs, 17-7 and 302/304. The 300 series stainless steels work harden only and not nearly as good as 17-7 stainless. do the 300 series ones have a tendency to look silvery and be inexpensive? I think I might have one in my “wtf is this” box.
Is loading a 30 round AR mag to 28 rounds instead of 30 and example of the above explanation? Will loading 28 rounds give the spring substantially longer life?
Not really. The difference in spring compression between 30 and 28 rounds is less than 3/8 inch, still far too close to solid for the spring's health.
I don't know is anybody makes action springs (or any AR springs) out of 302, or similar.
The action spring (and all the other SS springs in a AR) are supposed to have a passivated finish. To passivate SS you dip the part in a acid and etch off any free iron atoms on the surface, this make the parts more corrosion resistant. It also tends to make the surface look frosty.
Consumer 302 stainless stuff really does not get passivation treatment, as it is an expense. Your springs may be 302 or 17-7 and not passivated, which would make it shiny in appearence.
It would be interesting to see one of you guys take one of THESE (https://www.bexararms.net/gen2-ar15-fws/) for a whirl.
Here's why I don't mess with springs, and generally control things with the gas flow and buffer mass.
The initial bolt velocity is governed by the first 0.325 inch of carrier movement, the travel of the cam pin. The pressure in the cavity maxes out around 2,000 psi, with a 1/2" diameter piston, that generates a force of about 300 pounds. The spring is pushing forward with 6 pounds, that force is negligible, as the variation in pressure from round to round makes more difference than that. So, the bolt velocity is independent of the spring. The deceleration of the bolt carrier is governed by the mass of the bolt, carrier and buffer, as well as the force generated by the spring. The energy absorbed by the spring does not change that much, for example, the ones in the link above will absorb the same energy as a standard spring. These means changing the mass of the bolt/buffer assembly has more impact on final velocity. And the final velocity will always be positive when the buffer hits the back of the extension.
Since the buffer impacts the back of the extension, its velocity drops to zero, and all the forward velocity will come from the spring (and a small amount from the rubber tip rebounding). The spring cannot deliver more energy than it absorbed, and the rebound energy from the rubber tip on the buffer is the same, the forward velocity is also mostly governed by the mass.
(Although, I do concede that changing spring might allow finer adjustments, but I have never found that level of control necessary.)
“Just put oil on it” is silly, because the action spring is not a place where lubrication would be required if we could just stop tinkering. Saying that it’s the solution, is admission that there’s a problem, and I’m saying that problem doesn’t need to exist, because CS springs don’t solve any problem.
I don't use any CS action springs but I lubricate all of them, even stainless ones. Is there a good reason not to?
I don't use any CS action springs but I lubricate all of them, even stainless ones. Is there a good reason not to? Not that I’m aware of unless you’re in a high sand/dust environment.
I don't use any CS action springs but I lubricate all of them, even stainless ones. Is there a good reason not to?
Every so often check the end of the RE for any accumulation and clean it out. If you stand the gun on its butt CLP can migrate off the carrier etc and gravity never ceases, so a peek now and then never hurts. The carrier going back in there brings shit with it over time anyway.
Every so often check the end of the RE for any accumulation and clean it out. If you stand the gun on its butt CLP can migrate off the carrier etc and gravity never ceases, so a peek now and then never hurts. The carrier going back in there brings shit with it over time anyway.
I actually took apart my 605 not-clone today and found that the spring and buffer were slathered in black CLP. It spends most of its time sitting in the safe exactly as you describe, and I think lube migrates off the chromed carrier more than my phosphate carriers, which will migrate also. Ironically, I lube my guns minimally.
I actually took apart my 605 not-clone today and found that the spring and buffer were slathered in black CLP. It spends most of its time sitting in the safe exactly as you describe, and I think lube migrates off the chromed carrier more than my phosphate carriers, which will migrate also. Ironically, I lube my guns minimally.
I bet it would still run LOL.
Here's why I don't mess with springs, and generally control things with the gas flow and buffer mass.
The initial bolt velocity is governed by the first 0.325 inch of carrier movement, the travel of the cam pin. The pressure in the cavity maxes out around 2,000 psi, with a 1/2" diameter piston, that generates a force of about 300 pounds. The spring is pushing forward with 6 pounds, that force is negligible, as the variation in pressure from round to round makes more difference than that. So, the bolt velocity is independent of the spring. The deceleration of the bolt carrier is governed by the mass of the bolt, carrier and buffer, as well as the force generated by the spring. The energy absorbed by the spring does not change that much, for example, the ones in the link above will absorb the same energy as a standard spring. These means changing the mass of the bolt/buffer assembly has more impact on final velocity. And the final velocity will always be positive when the buffer hits the back of the extension.
Since the buffer impacts the back of the extension, its velocity drops to zero, and all the forward velocity will come from the spring (and a small amount from the rubber tip rebounding). The spring cannot deliver more energy than it absorbed, and the rebound energy from the rubber tip on the buffer is the same, the forward velocity is also mostly governed by the mass.
(Although, I do concede that changing spring might allow finer adjustments, but I have never found that level of control necessary.)
I concur. Very good analysis on the system. One thing to add is the vent holes in the bcg. That limits the active period gas impulse. Beyond that longer dwell time is not going to make any difference. That corresponds to the 0.325" bcg travel that determines the bcg speed.
The carbine spring in the other thread on action spring, K=1.53 lbf/inch", L0=10.7",L1=6.8",L2=3.2".
Energy the spring can store
Es=0.5*1.53*((10.7-3.2)^2-(10.7-6.8)^2)=31.4 lbf-inch
Work done on the bcg by the gas
Eb=300*0.325=97.5 lbf-inch
The spring is going to bottom out and the buffer is going to slam on the buffer tube end. I like setting up my gas to have the buffer just touch the tube end. That requires cutting the gas pressure by about half, with 25% margin to account for loss and energy required for extraction/feeding.
-TL
Sent from my SM-N960U using Tapatalk
Here's why I don't mess with springs, and generally control things with the gas flow and buffer mass.
The initial bolt velocity is governed by the first 0.325 inch of carrier movement, the travel of the cam pin. The pressure in the cavity maxes out around 2,000 psi, with a 1/2" diameter piston, that generates a force of about 300 pounds. The spring is pushing forward with 6 pounds, that force is negligible, as the variation in pressure from round to round makes more difference than that. So, the bolt velocity is independent of the spring. The deceleration of the bolt carrier is governed by the mass of the bolt, carrier and buffer, as well as the force generated by the spring. The energy absorbed by the spring does not change that much, for example, the ones in the link above will absorb the same energy as a standard spring. These means changing the mass of the bolt/buffer assembly has more impact on final velocity. And the final velocity will always be positive when the buffer hits the back of the extension.
Since the buffer impacts the back of the extension, its velocity drops to zero, and all the forward velocity will come from the spring (and a small amount from the rubber tip rebounding). The spring cannot deliver more energy than it absorbed, and the rebound energy from the rubber tip on the buffer is the same, the forward velocity is also mostly governed by the mass.
(Although, I do concede that changing spring might allow finer adjustments, but I have never found that level of control necessary.) I appreciate the detailed response. I love tech stuff.
Honestly, I just like the way the Bexar springs "feel."
Not only do they function perfectly, but they give the rifle a highER end feel when working the action.
I also throw a bit of OO grease in the tube.
My main AR (Aero receivers, BCG and tube) feels like the action is on roller bearings, though I know that's not just the spring. Also, instead of a"THWANG" sound and sensation, it drops with a really smooth, quiet and satisfying... "thunk."
It might sound dopey, but I really like it this way :cool:
The spring is going to bottom out and the buffer is going to slam on the buffer tube end. I like setting up my gas to have the buffer just touch the tube end. I shoot for that too.
I bet it would still run LOL.it does.
Energy the spring can store
Es=0.5*1.53*((10.7-3.2)^2-(10.7-6.8)^2)=31.4 lbf-inch
Work done on the bcg by the gas
Eb=300*0.325=97.5 lbf-inch
You have three times the amount of energy from the gas than the spring can absorb, in order to have thee "buffer just touch the tube end," you would need a spring with a spring rate of 4.75 lb/in. If you had a pre-load on the spring of 4 pounds (a little light), the force to cock the bolt back would be around 21 pounds. An MG-42 doesn't require that much force to lock the bolt back . . .
You get to bleed off about 1.0 to 1.1 fps bolt velocity with the spring. The buffer is going to hit the back of the extension with about 80% of its initial velocity. And if you want enough energy to extract, cock and cycle, you will need an initial bolt velocity of about 6.5 fps
You have three times the amount of energy from the gas than the spring can absorb, in order to have thee "buffer just touch the tube end," you would need a spring with a spring rate of 4.75 lb/in. If you had a pre-load on the spring of 4 pounds (a little light), the force to cock the bolt back would be around 21 pounds. An MG-42 doesn't require that much force to lock the bolt back . . .
You get to bleed off about 1.0 to 1.1 fps bolt velocity with the spring. The buffer is going to hit the back of the extension with about 80% of its initial velocity. And if you want enough energy to extract, cock and cycle, you will need an initial bolt velocity of about 6.5 fpsI don't plan to do that with stiff spring, but an adjustable gas block. :)
When come to think about it more, the primary extraction process would take up a bit more energy than I have thought. Say full 300lbf for 1/16" traveling would take out about 20 lbf-inch.
Also the gas impulse can't instantly pressurize the "gas cylinder". The pressure takes time to ramp up from zero to port pressure of 2000psi. It takes a big chunk out of the work done on the bcg+buffer.
Not sure about the exact figure, the weight in the buffer is lossy. It helps to some extend.
-TL
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I don't plan to do that with stiff spring, but an adjustable gas block. :)
When come to think about it more, the primary extraction process would take up a bit more energy than I have thought. Say full 300lbf for 1/16" traveling would take out about 20 lbf-inch.
Also the gas impulse can't instantly pressurize the "gas cylinder". The pressure takes time to ramp up from zero to port pressure of 2000psi. It takes a big chunk out of the work done on the bcg+buffer.
Not sure about the exact figure, the weight in the buffer is lossy. It helps to some extend.
-TL
Sent from my SM-N960U using Tapatalk
First, extraction takes place much faster than 1/16. Empirical data from tests shows the time for extraction is only about 1.5 ms, the energy loss is only about 1 lb-in.
Second, the fact that the pressure ramps up over a period of time does not change the total amount of energy delivered, only how fast the maximum is reached.
I don't have data on extraction. 1/16" is just a guess. Here I meant primary extraction. The fired brass to be pryed off the chamber wall, which requires quite a bit of effort. Looking at the primary extraction cam on a bolt action rifle, 1/16" travel doesn't seem too far off. 1 lbf-inch sounds low. Assuming 300lbf, the travel is only 0.003".
Gas pressure ramping up means the force on the bcg is not a constant 300lbf from beginning to end of the 0.325" travel. But rather it start from 0 and end up with 300lbf before the 0.325" runs out. It definitely bites a big chunk off the work done on the bcg.
-TL
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I don't have data on extraction. 1/16" is just a guess. Here I meant primary extraction. The fired brass to be pryed off the chamber wall, which requires quite a bit of effort. Looking at the primary extraction cam on a bolt action rifle, 1/16" travel doesn't seem too far off. 1 lbf-inch sounds low. Assuming 300lbf, the travel is only 0.003".
Gas pressure ramping up means the force on the bcg is not a constant 300lbf from beginning to end of the 0.325" travel. But rather it start from 0 and end up with 300lbf before the 0.325" runs out. It definitely bites a big chunk off the work done on the bcg.
-TL
Sent from my SM-N960U using Tapatalk
Yes, the work is different, but the energy is the same . . .
1 lb-in may be a bit high for a brass case . . .
https://i.imgur.com/PQNQCJA.png
Work done is amount of energy transferred.
The x-axis is time. We need distance traveled to calculate work done (energy). For brass it looks like 20lbf? Assuming 1/16" travel still, it would be 1.3 lbf-inch. Steel is 15x of that? No wonder they always overgas the gun.
Interesting. Thanks for sharing the info.
-TL
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Work done is amount of energy transferred.
The x-axis is time. We need distance traveled to calculate work done (energy). For brass it looks like 20lbf? Assuming 1/16" travel still, it would be 1.3 lbf-inch. Steel is 15x of that? No wonder they always overgas the gun.
Interesting. Thanks for sharing the info.
-TL
Sent from my SM-N960U using Tapatalk
Bolt velocity at time of extraction is about 20-25 fps.
https://i.imgur.com/mD3vDRV.png
Bolt velocity at time of extraction is about 20-25 fps.
https://i.imgur.com/mD3vDRV.png
Wow. I haven't seen information this detailed. Thanks.
I would say primary extraction happens when unlocking completes at about 2.3ms mark. End of piston motion means primary extraction completed and the bolt travels with the bcg at the same speed. That happens at 2.5ms mark. The displacement difference is about 0.8mm, or 0.031", or 1/32". Energy needed is 20*0.031=0.6 lbf-inch for brass and 9.3 lbf-inch for steel. You are right. My estimate was off by factor of 2.
Energy loss to extraction is indeed insignificant except for steel cased ammo. Looks like adjustable gas block is way to go.
-TL
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1) [/B]
Now, if you want to play with spring rates, and pre-loads, and C-S is the only offering available, that's fine, they will work just as well as anything else and last a long time if you take care of them. They might even be better because you can get the spring rate you want, but don't try and convince everyone they are better springs because they are C-S. They aren't.
_________________________
* Careful, there are two popular types of stainless steel for springs, 17-7 and 302/304. The 300 series stainless steels work harden only and not nearly as good as 17-7 stainless.
Was about to post exactly this. My entire use case for using Sprinco is that they are a known quantity when trying to tune a rifle to run suppressed. I keep a selection of them in sealed bags with a light coating of oil on them for just this purpose. And, when it comes to running an A5 setup, the Sprinco green seems to be the baseline when talking set ups.
Wow. I haven't seen information this detailed. Thanks.
I would say primary extraction happens when unlocking completes at about 2.3ms mark. End of piston motion means primary extraction completed and the bolt travels with the bcg at the same speed. That happens at 2.5ms mark. The displacement difference is about 0.8mm, or 0.031", or 1/32". Energy needed is 20*0.031=0.6 lbf-inch for brass and 9.3 lbf-inch for steel. You are right. My estimate was off by factor of 2.
Energy loss to extraction is indeed insignificant except for steel cased ammo. Looks like adjustable gas block is way to go.
-TL
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Nitpicky, but extraction starts at the end of piston motion (2.5 ms), when the cam pin bottoms out in the cam track. Only then does the bolt start to move.
What we have not taken into account is residual chamber pressure, depending on the timing of unlock there might be 200 psi residual chamber pressure. When the shoulder is uncorked from the chamber this will assist in extraction.
I normally ignore this as one, the force is low, and two, depending on the P-T curve used in the simulation, it sometimes isn't there.
Nitpicky, but extraction starts at the end of piston motion (2.5 ms), when the cam pin bottoms out in the cam track. Only then does the bolt start to move.
What we have not taken into account is residual chamber pressure, depending on the timing of unlock there might be 200 psi residual chamber pressure. When the shoulder is uncorked from the chamber this will assist in extraction.
I normally ignore this as one, the force is low, and two, depending on the P-T curve used in the simulation, it sometimes isn't there.Probably. But there really isn't any detectable slop in the slot for the cam pin to bottom out after unlocking position though. But if we define end of piston motion as bcg and bolt travel together, then you are correct.
There is one error I have noticed. The bcg speed is over 20fps, or 240 inch/s. It travels 0.36" in 1.5ms, which is way too long for primary extraction. The process must take shorter than that. The force plot shows distinct peak at 0.3ms for steel. Most likely it is when the casing breaks loose from the chamber. There is no peak for brass. The gauge probably was set to measure steel, and thus not sensitive enough for brass.
Distance traveled in 0.3ms is 0.072", or 1/16"! It doesn't change the conclusion. Energy loss to extraction is insignificant unless steel cased ammo is fired.
-TL
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shadowspirit
04-01-24, 19:55
It's all about making sure everything's in top shape and reducing the chances of any nasty surprises popping up later on. Trust me, it's worth it for the extra peace of mind knowing your gear's solid.
Yes..
shadowspirit
04-01-24, 19:58
Every so often check the end of the RE for any accumulation and clean it out. If you stand the gun on its butt CLP can migrate off the carrier etc and gravity never ceases, so a peek now and then never hurts. The carrier going back in there brings shit with it over time anyway.
Petroleum based lube or CLP does not migrate off things as readily as Breakfree CLP or other synthetic CLPs.
Strikefirst
04-03-24, 19:26
Where do you buy your standard srainless springs from?
The force plot shows distinct peak at 0.3ms for steel. Most likely it is when the casing breaks loose from the chamber. There is no peak for brass. The gauge probably was set to measure steel, and thus not sensitive enough for brass.
Distance traveled in 0.3ms is 0.072", or 1/16"! It doesn't change the conclusion. Energy loss to extraction is insignificant unless steel cased ammo is fired.
-TLCan you (and Lysander) expound more on the extraction differences in steel vs brass?
Where do you buy your standard srainless springs from?I buy Colt ones from Brownells, but I’m sure Colt or BCM ones would be just fine from BCM, Brownells, or Midway. VLTOR’s A5 spring is probably a rifle spring from BCM, so that’d probably be fine, too, in the appropriate receiver extension.
There is no peak for brass. The gauge probably was set to measure steel, and thus not sensitive enough for brass.
The test was specifically to measure the difference between the extraction force of brass cases vs steel cases. I will just quote the the report on why the difference in extraction force:
"During pressurization, the chamber of the gun expands radially in the elastic region and relaxes after the pressure dissipates to its original dimensions. However, the steel used in this analysis deformed plastically through most of the cartridge case during pressurization. Due to the level of the plastic deformation in the steel in the steel case, an interference fit occurs after elastic relaxation of the chamber. The radial force acting on the chamber due to the interference fit causes the steel case to stick in the chamber explaining the higher extraction forces. An example of this as related to the stress-strain curves of a material is shown in figure 14 . . . Switching to a steel with a higher yield strength may help solve this issue, but care must be taken to ensure the steel retains enough ductility to avoid case rupture."
https://i.imgur.com/SgkSOjl.png?1
"Pressurization and Extraction of a Steel and Brass Cartridge Case using Finite Element Analysis", Raymond Chaplin, ARDEC, Picatinny Arsenal, NJ, January 2017.
Also, friction between the chamber and case is greater for steel than brass. It should be noted that if the interference becomes to great, the case will stick fast in the chamber. Steel, as a case material, is much more sensitive to manufacturing tolerances than brass.
Oh, and the case-to-chamber fit does not actually have to be a hard interference (the case is larger than the chamber) in order to have high extraction forces. Here are the results from another extraction force study showing the extraction force required for a given case-chamber clearance:
https://i.imgur.com/oenCAoe.png
You can see that with a clearance of 0.0025" (diametrical) it will take 40 to 45 pounds to extract a brass case (zero residual pressure).
Oh, and the case-to-chamber fit does not actually have to be a hard interference (the case is larger than the chamber) in order to have high extraction forces. Here are the results from another extraction force study showing the extraction force required for a given case-chamber clearance:
https://i.imgur.com/oenCAoe.png
You can see that with a clearance of 0.0025" (diametrical) it will take 40 to 45 pounds to extract a brass case (zero residual pressure).There is clearance between casing and chamber before firing, as per saami, and force to extract a live round should be minimal. After firing, the clearance is gone as the casing expands under pressure. At zero pressure, the casing should spring back to restore part of the initial clearance to facilitate extraction. The amount of springing back is different for different metals. Brass is good. Mild steel is not so good. And hence rather different levels of extraction forces.
The chart for brass extraction doesn't seem making sense. Maybe I didn't read it correctly.
1. Why so much force required if there is clearance?
2. Why more force is required with zero pressure?
3. How can the extraction force be negative?
-TL
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There is clearance between casing and chamber before firing, as per saami, and force to extract a live round should be minimal. After firing, the clearance is gone as the casing expands under pressure. At zero pressure, the casing should spring back to restore part of the initial clearance to facilitate extraction. The amount of springing back is different for different metals. Brass is good. Mild steel is not so good. And hence rather different levels of extraction forces.
The chart for brass extraction doesn't seem making sense. Maybe I didn't read it correctly.
1. Why so much force required if there is clearance?
2. Why more force is required with zero pressure?
3. How can the extraction force be negative?
-TL
Sent from my SM-N960U using Tapatalk
The extraction force drops with increased clearance. At zero pressure, a clearance of 0.000", the extraction force is about 100 pounds, at a clearance of 0.005" the extraction force is nearly zero.
If there is pressure inside the chamber, it is pushing the case walls outward, but it is also pushing the case out of the chamber. The force pushing the case out of the chamber subtracts from the extraction force, if this chamber pressure force pushng the case out is greater than the friction force from the case-wall interaction, the extraction force will be negative.
The extraction force drops with increased clearance. At zero pressure, a clearance of 0.000", the extraction force is about 100 pounds, at a clearance of 0.005" the extraction force is nearly zero.
If there is pressure inside the chamber, it is pushing the case walls outward, but it is also pushing the case out of the chamber. The force pushing the case out of the chamber subtracts from the extraction force, if this chamber pressure force pushng the case out is greater than the friction force from the case-wall interaction, the extraction force will be negative.I see it now. Thanks.
It is still hard to understand why 2.5mil clearance still needs 40lbf. The 2 objects are out of contact already. There is air between them. Even with 5mil clearance (more than thickness of printer paper) the force is still non-zero. Where does the resistance come from? Carbon residues filling the clearance?
That aside, the graph gives insight to the difference between steel and brass casing extractions. The force vs. time graph you posted early indicates 20lbf for brass, and there is no peak in the curve. The brass case springs back so much that there is about 3mil clearance to the chamber wall. On the other hand, steel casing has little or no clearance.
-TL
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Here is some interesting unscientific data on actions springs that I have tested numerous times with my spring tester.
The Tubb Flat Wire in the chart is incorrect. It's only 10 lbs in condition 2. Not 16 lbs
71564
the AR-15 Junkie
04-07-24, 13:20
Here is some interesting unscientific data on actions springs that I have tested numerous times with my spring tester.
The Tubb Flat Wire in the chart is incorrect. It's only 10 lbs in condition 2. Not 16 lbs
71564
No difference between sprinco blue and sprinco red?
No difference between sprinco blue and sprinco red?
Nope.
I was surprised how little difference there was between all the AR15 carbine springs until you get to the Sprinco Green.
Of course the .308 caliber recoil springs are heavier...
Here is some interesting unscientific data on actions springs that I have tested numerous times with my spring tester.
The Tubb Flat Wire in the chart is incorrect. It's only 10 lbs in condition 2. Not 16 lbs
71564
Great post. Makes sense, given that I have a hard time telling some of Sprinco’s springs apart without the paint on them. Let me know if you’d like me to send you a Hot White, Colt rifle, and a Tubbs .308. A standalone thread with the op having a pretty complete list of springs tested on a single rig would be super cool. I’m sure someone has a G$ braided and a Strike flatwire floating around, too.
Great post. Makes sense, given that I have a hard time telling some of Sprinco’s springs apart without the paint on them. Let me know if you’d like me to send you a Hot White, Colt rifle, and a Tubbs .308. A standalone thread with the op having a pretty complete list of springs tested on a single rig would be super cool. I’m sure someone has a G$ braided and a Strike flatwire floating around, too.
Have you seen this?
This topic is relevant to my interests. As a mental exercise to satisfy my own curiosity, I had measured a few springs to try and understand how spring parameters might translate into AR15 operation and perceived recoil. In concept, the spring stores the recoil energy and the reciprocating mass changes the harmonic frequency of the spring-mass system. In my case, I just wanted to look at the spring variable.
I used a digital trigger scale to roughly measure the force, in pounds, at bolt closed position and after (x) inches compression. I did this by installing the respective spring into a lower receiver with the corresponding buffer and measured the force needed to push the buffer away from the buffer detent horizontally. Then I used an extension of known length (x) to push the buffer and tried to get the force after (x) compression. I averaged three to five measurements each time. Those numbers are F1 and F@x. Due to the limits of the trigger scale, I had to calculate the bottom-out force of F2 at 3.5" of bolt travel.
I also measured other spring characteristics like coil count, free length, coil diameter, etc. and used spring formulas to back-calculate linear spring rate (k) and stored energy (1/2 kx^2). The below table is the data I've collected so far. I haven't had any time to do any analysis beyond a brief review of it and I'm sure there are many problems with it.
The flatwire springs with (Calc) in the description are calculated A5 extension values using measurements in a carbine extension as a sanity check to compare with actual A5 measurements. They seem to correlate for the most part.
https://i.imgur.com/gT8kawx.jpg
There are some general observations I made from the data, although not precise due to the limits of my measurement system. I think there are valid general trends and physical principles.
Flatwire springs have a higher F1 due to the longer free-length and more initial compression. The flatwire allows the longer spring to fit within the confines of the buffer and receiver extension at full compression.
The A5 rifle spring follows a similar principle by using a longer free-length but instead, uses a longer extension to accommodate the longer coil spring.
Even at the same spring rate, longer springs with more initial compression can store more energy within the same 3.5" of bolt travel. This will reduce the bottom-out impact and therefore, felt recoil until it prevents full bolt travel and proper function.
Flatwire springs make a grinding sound and generally have more friction than coil springs in the same receiver extension.
indianalex01
05-01-24, 23:17
American Mediocrity and Contracts awarded to minorities! I remember this crap in the 90s with Sanchez and Coopers mags. As I understand it they would give the magazine tooling to various brown people so they could make money screwing up the military's magazines. American stupidity at its finest.
Dude are you being serious? Calling minority workers mediocre? Saying brown people screwed up military mags? Damn you are one Racist POS. I can’t believe nobody call that out. Damn.
Have you seen this? I did not; thanks. When y’all look at the variation among Tubbs springs, keep in mind that they changed from CS to SS at some point, which was a very good move.
Dude are you being serious? Calling minority workers mediocre? Saying brown people screwed up military mags? Damn you are one Racist POS. I can’t believe nobody call that out. Damn. I didn’t notice that the first time through the thread. I usually roll my eyes and keep scrolling when I see the “American mediocrity” catchphrase.
Dude are you being serious? Calling minority workers mediocre? Saying brown people screwed up military mags? Damn you are one Racist POS. I can’t believe nobody call that out. Damn.
Good catch.
Dude are you being serious? Calling minority workers mediocre? Saying brown people screwed up military mags? Damn you are one Racist POS. I can’t believe nobody call that out. Damn.
Are you being serious? In case you are, No. I'm not calling all non white/minorities mediocre workers. The practice of awarding contracts to incompetent people because the color of their skin is what I have issue with.
Shit. That idiot who had the mag company "Cprod" was, I assume, a white guy. And he put total garbage out on the market.
Are you being serious? In case you are, No. I'm not calling all non white/minorities mediocre workers. The practice of awarding contracts to incompetent people because the color of their skin is what I have issue with.
Shit. That idiot who had the mag company "Cprod" was, I assume, a white guy. And he put total garbage out on the market.
..........and that isn't actually a news flash either.
He just likes to stir up confrontation with many threads he's in........
Are you being serious? In case you are, No. I'm not calling all non white/minorities mediocre workers. The practice of awarding contracts to incompetent people because the color of their skin is what I have issue with.
Shit. That idiot who had the mag company "Cprod" was, I assume, a white guy. And he put total garbage out on the market.
I can verify that guy was a POS
Dude are you being serious? Calling minority workers mediocre? Saying brown people screwed up military mags? Damn you are one Racist POS. I can’t believe nobody call that out. Damn.
I think you have it backwards. Hes calling mediocre workers mediocre. They got the contract due to racism. I dont know the details he's talking about, but its industry standard at this point( DEI)
I honestly believe that the whole HPT/MPI thing was popularized by rob_s and his chart. Prior to "The Chart" as it has come to be known, practically nobody besides Colt did HPT/MPI to their barrels/bolts, and the only reason why Colt did so is because it was stipulated by the U.S. Army as per the M4's TDP, but then along came rob_s and his chart, then suddenly it became mainstream, companies began at least batch testing their AR Pattern Rifles/Carbines and using modified versions of "The Chart" without the authorization/consent of rob_s without crediting him for it in their marketing which upset him so badly they he did his best to delete all instances of "The Chart" that he had ever posted so that companies could no longer use it for marketing purposes, but by that point it had been reposted ad nauseum and left its mark on the industry.
To this very day, some still reference "The Chart" despite the fact that it is over a decade out-of-date, was inaccurate/incomplete even in its most recent iteration, and is functionally irrelevant to the modern AR Market since it effectively set a standard, ergo most ARs save for perhaps the absolute cheapest bargain basement ARs in current production seem to at the very least batch test their barrels/bolts, which was by far the biggest deal to the average consumer because stuff like H Buffers could be added later, and over time most folks came to accept nitrided barrels as a viable alternative to chrome-lining.
The very direction this thread has drifted into perhaps illustrates just how irrelevant HPT/MPI has become in the greater scheme of this because it is so commonplace now that it no longer has any bragging rights/prestige associated with it, ergo everyone has to use niche sidegrades like Chrome-Silicon Springs in their ARs to feel superior to the average AR owner because all of the meaningful, arguably necessary upgrades to the ARs of years past come standard in just about every AR or otherwise can be added down the line at negligible expense by the end-user.
indianalex01
05-04-24, 02:59
I can verify that guy was a POS
You condone talking about minorities like that too? You are a POS.. shame on all of you for condoning that racist crap.
..........and that isn't actually a news flash either.
He just likes to stir up confrontation with many threads he's in........
Yea go ahead and lieÂ…. Unbelievable how some of you are ok with his statements.
For the racist and the people supporting the racist.. show me a military contract that got screwed up because unqualified minorities were working for said contracting company. I havenÂ’t seen one.. itÂ’s a shame that some of you agree with the poster who put down minority Americans. IÂ’m a minority and made it to the top in the Corps. DonÂ’t post some BS that is minorities donÂ’t do a good job and or incompetent. Shame on all of you for supporting him. Show me FACTSÂ…. You wonÂ’t find them. It chaps my ass that is this day in America we have such blatant racism. IÂ’m the bad guy because I call it outÂ…
2 people agreed with meÂ….
You condone talking about minorities like that too? You are a POS.. shame on all of you for condoning that racist crap.
Yea go ahead and lieÂ…. Unbelievable how some of you are ok with his statements.
For the racist and the people supporting the racist.. show me a military contract that got screwed up because unqualified minorities were working for said contracting company. I havenÂ’t seen one.. itÂ’s a shame that some of you agree with the poster who put down minority Americans. IÂ’m a minority and made it to the top in the Corps. DonÂ’t post some BS that is minorities donÂ’t do a good job and or incompetent. Shame on all of you for supporting him. Show me FACTSÂ…. You wonÂ’t find them. It chaps my ass that is this day in America we have such blatant racism. IÂ’m the bad guy because I call it outÂ…
2 people agreed with meÂ….
Go away.
Anyone who's worked in a large company has seen and had enough of the diversity BS.
Earn it.
I'm now done with your BS. Buh Bye.
indianalex01
05-04-24, 11:05
Go away.
Anyone who's worked in a large company has seen and had enough of the diversity BS.
Earn it.
I'm now done with your BS. Buh Bye.
Oh yea big racist punk telling people to go away. America is the greatest of all time. Love it get out. Bye bye..
Somebody please close this f***ing thread, have mercy. Anybody want talk about guns?
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